1. Field of the Invention
The present invention relates to a sealed container and a sealed container ambient gas substitution apparatus and method for substituting the ambient gas in the sealed container.
2. Description of the Related Art
Electronic substrates, e.g., semiconductor devices, liquid crystal devices and magnetic disks, are manufactured in a clean room free from dust, and are conveyed from one step to another in the clean room while a cassette accommodating the electronic substrates is accommodated in a portable sealed container, in order to prevent contamination that occurs when molecules of organic substances, boron or phosphorus are adsorbed by the electronic substrates.
In recent years, in order to prevent not only contamination that occurs when the molecules of organic substances or the like are adsorbed by the electronic substrate, but also growth of the native oxide on the surfaces of the electronic substrates, the cassette is accommodated in a portable sealed container, the internal ambient gas of which is substituted with an inert gas, e.g., nitrogen or argon, to decrease the oxygen concentration, and the electronic substrates are conveyed in this state.
FIG. 1 shows a semiconductor wafer portable sealed container which is used in the semiconductor device manufacturing process, a semiconductor wafer cleaning unit and a portable sealed container ambient gas substitution unit mounted on the cleaning unit. In a portable sealed container 11, a cassette 13 accommodating semiconductor wafers 12 is placed on a bottom plate 14, and the bottom plate 14 and a housing 15 are fitted with each other to form a sealed space.
An opening 17 is formed in the upper surface of an ambient gas substitution apparatus 16, and the peripheral portion of the opening 17 forms a work table 18 for the portable sealed container 11. When the portable sealed container 11 is placed on the work table 18, the bottom plate 14 and the cassette 13 are moved downward by an elevator 19 while leaving only the housing 15 on the opening 17. The semiconductor wafers 12 are extracted from the cassette 13 one by one, and are conveyed into a cleaning unit 21.
A cleaning cup 22 is arranged in the cleaning unit 21, and a cleaning chuck 23 and a cleaning nozzle 24 are arranged in the cleaning cup 22. A semiconductor wafer 12 cleaned by the cleaning unit 21 is conveyed in the sealed space to be returned to the cassette 13 in the ambient gas substitution apparatus 16. Then, the bottom plate 14 and the cassette 13 are moved upward by the elevator 19.
Immediately before the bottom plate 14 closes the opening 17 to form a sealed space together with the housing 15, the elevator 19 is stopped once, and the ambient gas substitution apparatus 16 substitutes the ambient gas in the portable sealed container 11 with nitrogen. When the oxygen concentration in the portable sealed container 11 reaches a predetermined value, e.g., 10 ppm, the elevator 19 is moved upward again and the bottom plate 14 and the housing 15 are fitted to each other to form a sealed space.
Thereafter, the portable sealed container 11 is removed from the ambient gas substitution apparatus 16, and is conveyed to a next-step unit, e.g., an oxidation unit or film formation unit. The semiconductor wafers 12 are processed in the sealed space in this step as well. Between the respective steps, the semiconductor wafers 12 are conveyed as they are accommodated in the portable sealed container 11, the ambient gas of which has been substituted with clean nitrogen which is purified by filtration.
FIG. 2 shows a portable sealed container 11 according to one related art and the main part of an ambient gas substitution apparatus 16 according to one related art. One end portion of a nitrogen supply pipe 25 is located at a portion of the periphery of an opening 17 of the ambient gas substitution apparatus 16 of this related art, and the other end portion of the nitrogen supply pipe 25 is connected to a nitrogen gas line through a gas supply valve 26. One end portion of an exhaust pipe 27 is located on a side of the periphery of the opening 17 which is opposite to one end portion of the nitrogen supply pipe 25, and the other end portion of the exhaust pipe 27 is connected to an exhaust duct through an exhaust valve 28.
When an elevator 19 is stopped immediately before a bottom plate 14 closes the opening 17 to form a sealed space together with a housing 15, as described above, in order to substitute the ambient gas in the portable sealed container 11 for nitrogen, the gas supply valve 26 and the exhaust valve 28 are opened. As a result, nitrogen is supplied from the nitrogen gas line into the portable sealed container 11 through the nitrogen supply pipe 25. The ambient gas in the portable sealed container 11 is pushed to the outside through the exhaust pipe 27, and the oxygen concentration of the ambient gas in the portable sealed container 11 is accordingly decreased. Thereafter, the gas supply valve 26 and the exhaust valve 28 are closed.
As shown in FIG. 2, in the portable sealed container 11 and ambient gas substitution apparatus 16 of these related arts, a nitrogen flow 29 in the portable sealed container 11 is a turbulence, and the ambient gas that fills the portable sealed container 11 and nitrogen supplied from the nitrogen supply pipe 25 are mixed. Therefore, the ambient gas that fills the portable sealed container 11 is not efficiently discharged through the exhaust pipe 27. To substitute the ambient gas in the portable sealed container 11 with nitrogen takes a long period of time, and it is difficult to completely substitute the ambient gas in the portable sealed container 11 with nitrogen.
If substitution of the ambient gas in the portable sealed container 11 takes a long period of time, not only is the semiconductor device manufacturing time prolonged, but also the amount of nitrogen to be supplied from the nitrogen supply pipe 25 is increased, resulting in a high semiconductor device manufacturing cost. If the ambient gas in the portable sealed container 11 cannot be completely substituted with nitrogen, contamination caused by adsorption of organic substances or the like and growth of the native oxide during conveyance are likely to occur, and the quality, e.g., electrical characteristics, of the semiconductor devices is decreased to decrease the yield. This also increases the semiconductor device manufacturing cost.